Hybrid microchip bonding article

ABSTRACT

An article for tape-automated bonding of integrated circuit microchips comprises a carrier sheet (22) carrying conductive tracks (23) with a tubular metal formation (21) passing through the sheet at the end of each track for connection to a microchip (24). The tubular formations tend to accommodate irregularities in the chip and may contain solder or other metal having a lower melting point than the tubular formation to effect bonding.

FIELD OF INVENTION

This invention relates to a hybrid bonding article which can be providedin arrangements suitable for use in tape-automated bonding (TAB) ofsemiconductor microcircuits (microchips).

INTRODUCTION TO INVENTION

Known TAB devices have a structure akin to that shown schematically inthe accompanying sketch A. A polymer tape A1 having edge sprocket holesA2 for feeding the tape in automated bonding equipment carries a seriesof arrays (one shown) of conductive tracks A3 arranged in a patternsuitable for bonding their inner ends A4 to the bonding sites of amicrochip (not shown). The tape A1 is cut away under the ends A4 of thetracks so that the ends project as unsupported "flangers" over thecut-away space A5. Bonding is effected by bending the flangers into thespace A5 to make contact with the chip positioned against the oppositeside of the tape from that carrying the tracks. This is followed bybonding by known techniques which often require the chip bonding sitesto "bumped" with bonding material, e.g. solder.

The present invention can avoid such disadvantageous "bumping"processes.

Another form of TAB device known as "area TAB" is described in U.S. Pat.Nos. 3,832,769, 3,868,724 and 4,472,876, in which the conductive tracksdo not project as "fingers", but instead are connected to solid metalterminals formed in holes passing through the tape material. Theterminals project from the surface of the tape remote from the tracksand can therefore make electrical contact with bonding sites on microchips or other devices brought into contact therewith. The reliabilityof the electrical contacts thus established may be limited by therelative rigidity of the terminals hindering their ability to conform tovariations in height of the bonding sites on the chip, especially asincreasing miniaturization and complexity of microchips requires bondingsites in central areas of the chip as well as around its edges.

SUMMARY OF THE INVENTION

The present invention alleviates these problems by means of an ingenioushybrid form of TAB article, and accordingly provides in one of itsaspects a tape-automated bonding article comprising a carrier sheetcarrying at least one array of electrically conductive tracks havingends arranged for bonding to a microcircuit device, each such bondabletrack end being supported by the carrier sheet material and beingelectrically connected to a surface region of the carrier material notcarrying that track end by a tubular formation of electricallyconductive material within, preferably plated within, at least oneconnecting hole of diameter less than 200 micrometers, preferably lessthan 100 micrometers, more preferably less than 50 micrometers. Theholes will usually pass more or less straight through the sheet to itsopposite surface (i.e., the "surface region not carrying the trackend"), but may be sloping or indirect (e.g. curved) if desired.Preferably, the tubular conductive material in the connecting hole orholes projects beyond the said surface region so as to facilitatebonding to the microcircuit, and this may be achieved by removing one ormore layers from the carrier sheet after plating (or other provision) ofthe conductive material in the connecting hole.

The use of a tubular formation of conductive material (preferably metal)in the connecting holes has considerable advantages over the known solidmetal terminals. The tubes may crumple when compressed longitudinallyagainst a microchip or other device, thus taking up irregularitieswithout the major deviation from the longitudinal axis which normallyresults when solid columns or wires are so compressed. Also, solder orother fusible material may be provided at or within the ends (at least)of the tubes to facilitate thermal bonding and electrical connection.

This hybrid TAB article according to the invention may be constructedwith cut-away "fingers" of the carrier sheet material supporting theconductive track ends to be bonded, thus providing a "fingered"construction corresponding to, but with advantages over, the ordinaryTAB article; or may be constructed with "fingers" extending also to thecentral regions of the chip. These "fingered" hybrids may be regarded asa separate aspect of the invention, for which alternative forms ofconnection (e.g. solid wires or posts) may also be useful. Cutting awaythe carrier is not essential, since the tubular projections from theconnecting holes can be arranged to render unnecessary the bending ofthe track ends, but the "fingered" construction may provide advantageousflexibility in articles with central, as well as peripheral, connectionsites.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 shows in plan view a tape-automated bonding (tab) articleaccording to the present invention;

FIG. 2 shows a form of tab article not having the cut-away fingers ofthe present invention;

FIG. 3 shows schematically a tab production line;

FIG. 4 shows schematically in enlarged detail part of FIG. 3;

FIG. 5 shows schematically in enlarged detail a tab article in use witha microchip embedded in a support substrate;

FIG. 6 shows schematically a laminar sheet for making a multi-level tabarticle;

FIG. 7 shows schematically an article made from the laminate of FIG. 6in use with a microchip;

FIG. 8 shows a plan view of a prior art tape-automated bonding (tab)article.

DETAILED DESCRIPTION OF INVENTION

An example of a fingered construction accordingly to the presentinvention is illustrated schematically in FIG. 1 of the accompanyingdrawings, wherein the reference numerals correspond to the numerals usedin FIG. 8.

The connecting holes with the tubular electrically conductive material,preferably metal, therein, one or more per track end, cannot be made bythe methods described in the known "area TAB" patents mentioned above.The present invention preferably hybridizes the TAB concept with methodsand materials for making self-supporting uniaxial connectors describedin any one or more of copending British Patent Applications 8802567,8802565, 8802566, 8802568, 8815447.1, and European Published PatentApplications EP-A-0213774, 0327399, 0329314 and 0327398, the disclosuresof all of which are incorporated herein by reference. Laser ablationdrilling of a layered polymer sheet and metal plating within the hole(s)followed by removal of one or more soluble layers from the sheet (toexpose the ends of the metal tubes thus formed within the holes) ispreferred. The resulting hybrid TAB article incorporating in situtubular uniaxial connectors, with the metal TAB tracks preferablysubsequentially applied to its surface, represents a significantcommercial advance, as aforesaid, over previously proposed TAB articles.

These and other aspects of the invention are illustrated in the largelyself-explanatory FIGS. 2 to 7 of the accompanying drawings, and theinvention includes any novel sub-set or sub-combination of the featuresdisclosed in the drawings or description of this specification.

FIG. 2 illustrates schematically the use of a TAB article according tothe invention with central connection sites but without the easilyenvisaged cut-away "fingers". Metal tubes 21 project from holes througha polyimide sheet 22, with conductive tracks 23 connecting to the tubes.A standard unbumped I.C. is shown in position for thermocompression (orother) bonding to the hybrid TAB article.

FIG. 3 illustrates schematically a TAB production line in which apolyimide tape article 31 according to the invention with projectingplated metal tubes 32 is assembled with unbumped integrated circuitchips 33. The tape 31 is fed from left to right (as shown) by means notshown, passing under guides 35, and is bonded to the chips 33, feedingfrom right to left, by thermode 34.

FIG. 4 shows in more detail part of the TAB article and chip of FIG. 3(inverted), with metal tracks 41 on the surface of tape 31.

FIG. 5 shows a TAB article with a chip 33 inset in a support substrate51, the metal tubes 32 in this case electrically bridging, via thetracks 41, between the chip 33 and the substrate 51.

FIG. 6 shows a multilayer polymer/metal laminate suitable for making amulti-level TAB article (see FIG. 7) according to the invention. Coppertrack-forming layers 61 and 62 are provided on the opposite faces ofpolyimide sheet 53, with an optional further layer 64 of polyimide and asoluble layer 65 (e.g. of polyamide). The polyimide and soluble polymerlayers may be those described in the aforementioned British applicationsand published European applications.

FIG. 7 shows the use of a multi-level hybrid TAB article made bydrilling and plating the laminate of FIG. 6, (optional layer 64 omitted)followed by removal of the soluble polymer layer 65. Such a structurepermits closer spacing of the metal tubes 71 to connect to high densityI.C. 72 (standard unbumped form).

The hybrid TAB articles according to the present invention canadvantageously be impedance matched with the other circuitry to beconnected. Multi-layer articles (e.g. FIG. 7) could advantageouslyseparate signals from power, and very fine separation (pitch) betweentracks may be achieved.

When the sheet which ultimately contains the conductive through-holes(as distinct from any removable surface layers on such a sheet) is tocomprise a polyimide material, a preferred polymer material is asubstantially fully cyclised polyimide capable of retaining at least50%, preferably at least 75%, more preferably at least 85%, of itsoriginal elongation after immersion in water of pH10 at 100° C. for 4days according to ASTM D882. It will be readily understood that a"substantially fully cyclised" polyimide is one having substantially noopen imide rings or uncyclised amic acid groupings. Such a polyimide isbetter able to survive hot alkaline metal plating baths, which attackincompletely cyclised polyimides such as Kapton (TM).

The currently preferred commercially available polyimides are thoseavailable under the Trade Mark "UPILEX" from Ube/ICI. One of these,"UPILEX R", is believed to be a relatively completely cyclised polymerhaving a repeat unit derived from biphenyl dianhydride anddiaminodiphenylether, viz. ##STR1##

Preferred, however, is "UPILEX S", which is believed to have a repeatunit derived from the same anhydride and phenylene diamine, viz.

We claim:
 1. A tape-automated bonding article comprising a carrier sheethaving first and second main surfaces, the first surface carrying atleast one array of electrically conductive tracks having ends arrangedfor bonding to a microcircuit device, each such track end beingelectrically connected to the second surface of the carrier sheet by atubular formation of electrically conductive material within at leastone connecting hole of a diameter less than 200 micrometers, whichtubular formation is bondable to the microcircuit device in use toconnect the track end electrically thereto.
 2. An article according toclaim 1, wherein the tubular conductive sheet in the connecting hole orholes projects beyond the said surface region so as to facilitatebonding to the microcircuit.
 3. An article according to claim 1 havingconductive tracks on more than one level within its laminar structure.4. An article according to claim 1, having at or within that end of atleast some of the tubular formations which is to be bonded to themicrocircuit in use fusible electrically conductive bonding materialwhich can be fused to effect bonding at a fusion temperature lower thanthat of the tubular material.
 5. An article according to claim 2,wherein the fusible material is a solder or similar low-melting-pointmetal alloy.
 6. An article according to claim 1, wherein the carriersheet comprises a substantially fully cyclised polyimide capable ofretaining at least 50% of its original elongation after immersion inwater of pH10 at 100° C. for 4 days according to ASTM D882.
 7. Anarticle according to claim 1, wherein the at least one connecting holeis formed by laser ablation drilling and wherein at least one layer ofat least one metal is plated on the interior surface of the holes.